Conventionally, a main role of devices supporting electronics and information apparatus has been played by a Si semiconductor, and by means of the integrated circuit thereof, development of numerous products such as an electronic apparatus, a computer, a communication apparatus, and a domestic product has been achieved. As drawback of the Si semiconductor, there are, however problems such as that it is not light emitting, that the device size is limited by a wafer size, and that it is heavy. As a result, a compound semiconductor has been developed as a light emitting device, and an amorphous or polycrystal Si semiconductor has been developed as a large area panel.
Due to this situation, a study on an organic device has been developed, which aims at realization of an electronics and information apparatus having features such as large scale, light weight, space-saving, and flexibility. So far the organic material is characterized in a plenty of different material species of more than several millions as well as generation of novel functions, and technological fields such as an organo-electronic photosensitive material and a liquid crystal display device has been established so far. In recent years, aiming at a self light emitting device which is a complement to the liquid crystal display device, an attention is put on an organic EL device, and a development is in progress to realize a small scale display panel. As a subsequent development, a study has started on a novel organic device such as an organic transistor, an organic solar cell and an organic photodiode. Further research and development as well as establishment of a new industry are expected.
The organic EL device, the organic solar cell and the organic photodiode described above are realized from a device having a single or multiple layer structure of an organic material, and, in accordance with the category of the semiconductor device, they belong, in principle, to a diode having a p-n junction, a Schottky junction or the like.
FIG. 1 shows schematically a current-voltage characteristic of an organic diode.
In a dark condition without light irradiation, it exhibits a typical diode characteristic. In the conventional semiconductor device, there exists an ohmic contact at a metal—semiconductor interface, and there also exists carriers, the density thereof being in proportion to the impurity concentration in the semiconductor. On the other hand in the organic material in general, the difference between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) is larger than that of the Si semiconductor. Due to this, an interface between a metal and an organic semiconductor is of Schottky type or of a tunnel injection type, and the inside of the semiconductor is a conductive state with much less carrier concentration as compared to a Si semiconductor. Therefore, the expression of the characteristics is different from a Si, nevertheless the current—voltage characteristic is diode—like as same as the Si diode. Referring to FIG. 1, it is understood that the first quadrant is a light emission region of an organic EL device, the third quadrant is an organic photodiode region, and the fourth quadrant is a solar cell region. By taking these points into consideration, it can be contemplated that a device having simultaneously a light emission function and a photo sensing function could be realized. As a matter of fact, by using the same structure as a perylene tetracarboxylic derivative (PV)/copper phthalocyanine (CuPc) structure which C. W. Tang reported in 1986 (Refer to Non-Patent Document 1 below), Adachi reported an observation of light emission phenomenon of “a weak red light” (Refer to Non-Patent Document 2 below). In addition, by considering simultaneously an experimental result on an organic EL device of a conductive polymer (poly([2-methoxy-5-(2′-ethylhexyloxy)]-1,4-phenylenevinylene), MEH-PPV system made by a spray method by Echigo et al., (Refer to Non-Patent Document 3 below) and an experimental result of a top absorption type organic photodiode using the same material by Shimada et al. (Refer to Non-Patent Document 4 below), it can be contemplated that an organic diode having simultaneously a light emission function and a photo sensing function could be realized by using a single layer of the MEH-PPV.
Furthermore, as a stacking structure of a plurality of devices, there is a report by Chikamatsu on the stacking of an organic EL device and an organic photodiode (Refer to Non-Patent Document 6 below). In addition, there was a report given by Time Warner Entertainment Co. L.P. on realizing a light emission and a power generation by a multilayer structure of organic thin films (Refer to Patent Document 1 below), and a report was also given by Tsutsui et al., on an organic semiconductor device characterized in combining a functional film and a conductive thin film layer to improve the device characteristics (Refer to Patent Document 2 below).    [Patent document 1] Japanese Published Unexamined Application 2002-008851.    [Patent document 2] Japanese Published Unexamined Application 2003-264085.    [Non-Patent document 1] C. T. Tang: Appl. Phys. Lett., 48(2), 183, (1986).    [Non-Patent document 2] Adachi: M&BE, 14(4), 205, (2003).    [Non-Patent document 3] Echigo, Naka, Okada, and Onnagawa: “Organic EL device of conductive polymer by a spray method” Extended Abstracts (The 49th Spring Meeting, 2002); The Japan Society of Applied Physics, 27p-YL-16, (2002).    [Non-Patent document 4] Shimada, Naka, Okada, and Onnagawa: “Top absorption type organic photodiode intended for integration” Extended Abstracts (The 51st Spring Meeting, 2004); The Japan Society of Applied Physics, 31a-ZN-13, (2004).    [Non-Patent document 5] Y. Matsushita, H. Shimada, T. Miyashita, M. Shibata, S. Naka, H. Okada and H. Onnagawa: “Organic Bi-function Matrix Array” Extended Abstracts of Solid State Devices and Materials, pp. 168-169, (2004).    [Non-Patent document 6] M. Chikamatsu, Y. Ichino, N. Takada, M. Yoshida, T. Kamata, and K. Yase: Appl. Phys. Lett. 81, (2002), 769.